Wednesday, August 1, 2018

s390x changes in QEMU 3.0

QEMU 3.0 is currently in the late -rc phase (with the final release expected early/mid August), so here's a quick summary of what has been changed for s390x.

CPU models

A CPU model for the z14 Model ZR1 has been added. This is the "small", single-frame z14.

The feature bits for Spectre mitigation (bpb and ppa15) are now included in the default CPU model for z196 and up. This means that these features will be available to the guest (given the host supports them) without needing to specify them explicitly.

Devices

You can now configure consoles via -serial as well.

vfio-ccw devices have gained a "force-orb-pfch" property. This is not very useful for Linux guests, but if you are trying to use vfio-ccw with a guest that does not specify "unlimited prefetch" for its requests but does not actually rely on the semantics, this will help you. Adding support to vfio-ccw to accommodate channel programs that must not be prefetched is unfortunately not straightforward and will not happen in the foreseeable future.

Booting and s390 bios

The s390-netboot image has been enhanced: It now supports indirect loading via .INS files and pxelinux.cfg-style booting.

The boot menu can now also deal with non-sequential entries.

Miscalleneous

Handling of the TOD clock in tcg has been improved; CPU hotplug under tcg is now working.